1. Field of the Art
This invention relates to an apparatus for analyzing the correlation between the molecular weight and the chemical structure or the molecular structure of polymers within short periods of time.
In general, polymers are mixtures in which any one or all of the molecular species such as molecular weight, chemical composition, molecular structure and the like, are nonhomogeneous. The quality of a polymer is usually determined by these molecular species. It is therefore indispensable to obtain proper distribution data concerning these molecular species for studies to improve the quality of polymers.
Gel permeation chromatography (GPC), the fractional precipitation or dissolution method, and other polymer fractionating methods are performed for this purpose. These fractionating methods, however, only give data concerning any one of the above molecular species. If a correlation is found between two or more molecular species, a higher level of molecular design will be possible. For this purpose, it may be suggested to combine two or more fractionating means together. In this case, however, two or more different fractionating methods must be carried out in a two-dimensional manner. That is, a given molecular species is first fractionated, according to a given fractionating method and then the obtained fractions are subjected to other fractionating methods, requiring laborious work and extended periods of time (usually more than one week).
2. Background Art
The so-called column method, which belongs to the category of the fractional dissolution method, has been proposed for determining the distribution of methyl branches (distribution of composition or, in this case, crystallinity distribution) in polyethylene ("Polymer Preprints", Vol. 18 (2), 1977, pp. 182-187). Thus, a polymer solution is passed through a small column filled with an inert filler (chromosorb P) such that the surface of the filler is coated with the polymer. Next, the temperature of the column is continuously raised to elute the polymer in the order of increasing crystallinity or decreasing methyl branches, and the eluates are introduced into a differential refractometer to obtain a distribution curve of methyl branch from the data from the differential refractometer and the column temperature (the number of methyl branches decreases with increase in column temperature). The above literature teaches that the methyl branch distribution (crystallinity distribution) and the molecular weight distribution should preferably be combined together, but does not disclose any specific examples.
On the other hand, the method in which the column is filled with a porous filler and a polymer solution passed therethrough to elute the polymer in the order of decreasing molecular sizes, is called the GPC method and has been widely used for determining the molecular weight distribution of the polymer (Aldgeld et al., "Gel Permeation Chromatography", published by Marcell Decker Co., U.S.A., 1971).
If these two methods are combined together, the correlation can be analyzed between the chemical structure or molecular structure of a polymer and the molecular weight distribution. However, the aforementioned problem with regard to the speed of analysis is not solved even if they are simply combined together, i.e., for example, a polymer is fractionated depending upon the molecular structure using the fractional dissolution column method and then the molecular weight distributions are determined for each of the obtained fractions by the GPC method.
In order to solve the above-mentioned problem, i.e., to carry out two-way fractionation consisting of molecular composition fractionation and molecular size fractionation within short periods of time, the present inventors have already proposed a method in Japanese Patent Publication No. 7975/1987. This method comprises precipitating a polymer to be analyzed on a filler in a column, eluting the precipitated polymer while stepwisely raising the temperature, and batchwisely sending the polymer fractions fractionated at each temperature step into a molecular weight distribution analyzer, in effecting composition fractionation by the fractional dissolution column method. The above publication further introduces an apparatus for concretely putting this method into practice. This apparatus comprises a composition fractionation unit A provided with a fractional dissolution column for effecting the stepwise fractional dissolution and a flow path change valve, a molecular size fractionation unit B for fractionating, depending on the molecular size, the polymer that is fractionated by the unit A, a solvent feeding unit C that feeds to the units A and B a solvent for use in the fractional dissolution of the sample polymer and for transferring the polymer solution, and a detection unit D for detecting the results of fractionation obtained in the unit B, and wherein an automatic temperature controller and a valve controller are connected to the unit A.
This apparatus draws attention from the standpoint of effectively putting the above-mentioned method into practice, but is not satisfactory for practical use. For example, the sealing performance of the valves for changing flow path decreases since the valves and the composition fractionation column, which undergoes great temperature change, are accommodated in the same unit. Furthermore, there is no mechanism for confirming the performance of the column and the constant displacement of pumps. This apparatus thus involves serious problems in the lowering of the measuring precision and in the maintenance of the apparatus when the operation is continued for extended periods of time.